Typically, a header for a harvesting machine includes a cutterbar which is operable to cut standing crop as the machine moves forward and a rotatable reel which carries tines to engage the standing crop and sweep it towards the cutterbar for cutting and then carry the cut material towards an auger before releasing it. The auger usually consolidates the cut crop material centrally of the header before it is passed to the body of the machine for processing. The distance between the cutterbar and the auger is critical and in general the optimal position depends on the type and condition of the crop to be harvested. Therefore some header types have been provided with a cutterbar mounted to a forwardly extendable cutting table, enabling the operator of the harvesting machine to adapt its configuration when the crop condition or type changes.
When harvesting down crops, i.e., crops that are not standing in a normal upright position, the relationships between the reel, the cutterbar and the auger is equally critical and, in general, the reel should be disposed so that the path described by the outer ends of the tines first enters the down crop forwardly of the cutterbar and below the level thereof for lifting the crop, then sweep closely over the cutterbar and finally pass in close proximity along the auger.
Headers are known in which the cutterbar is vertically flexible along its length so that it can follow local irregularities in the ground. With such headers, it is necessary to be able to adjust the height of the reel relative to the highest point of the cutterbar at any given instant, otherwise the cutterbar is likely to foul the reel on flexing with consequential damage to one or both components. To this end, headers having flexible cutterbars have been fitted with means for automatically adjusting the position of the reel on vertical flexure of the cutterbar.
Similar problems may occur when the cutterbar of an extendable header is set to forwardmost position. Then the cutterbar will enter into the reel path that is required otherwise for harvesting down crops with a retracted cutting table. The tines or the bars of the reel may then damage the cutterbar or vice versa. Measures must be taken to prevent such interference and limit the path of the reel tines when the header is extended.
EP-A-0 250 649 describes an interlock mechanism including a linkage mechanism between the movable cutting table and the hydraulic actuators on each side of the header that position the reel in a vertical direction. The interlock mechanism includes a bell-crank lever pivotally mounted on the corresponding header side wall. The linkage interconnects the cutterbar and the lever, whereas the other lever arm holds the lower end of the actuator. The mechanism adjusts the position of the actuator and hence of the reel in response to a fore-and-aft adjustment movement of the cutterbar so as to maintain the minimal spacing between the reel and the cutterbar substantially constant.
Another existing mechanism, as used in the Varifeed™ headers of New Holland, uses a cam system for limiting the vertical position of the reel arm. The system comprises a linkage whereby a first arm is fixed to the movable cutterbar table and a second arm is fixed to the frame below the reel arm. At the end of the second leg a cam is fixed which makes contact with a roller installed on the reel arm when this arm is lowered. When the cutterbar moves forward, the first leg will pull on the second leg and rotate the cam, thereby pushing the roller upwards. As such, the reel arm is pushed upwards, hereby lifting the reel and avoiding interference with the cutterbar.
These known systems have some disadvantages. The connection point between the reel arm and the interlock mechanism, or the contact point between the cam and the roller is close to the rotation point of the reel arm. Considering the weight of the reel and the accelerations caused by operation on a bumpy field, the load on the interlock mechanism or the cam is high. Furthermore, the load is transferred directly to the frame, which is not advantageous for frame deformation and lifetime. Another disadvantage for the cam system is that the hydraulic lift cylinder is fixed to the frame, while the reel arm can be forced upwardly by the cam. Hereby, when extending the header and lifting the reel, the cylinder rod gets pulled outwards little resulting in oil or air getting drawn through the sealing of the cylinders.
As illustrated by DE-A-195 08 887, it is also conceivable to provide a sensor on the reel arm for contacting a cam surface on the movable cutterbar table when the cutterbar is extended. A control system reacts to the contact signal of the sensor by loading the hydraulic actuator and raising the reel arm until the sensor is disengaged from the cam. Such system entirely relies on the proper and continuous operation of the sensor, which is positioned in a vulnerable forward position close to the crop. Hence, it does not have the reliability of mechanical systems. Furthermore, it limits the available stroke of the actuator and the consequent vertical range of the reel.
It is an object of the present invention to provide a header with a fore-and-aft adjustable cutterbar to suit various crops and crop conditions and which avoids interference between the reel and the cutterbar upon adjustment of the cutterbar.